1. Field of the Invention
This invention relates to a method and a sensor for detecting chemical substances contained in a vapor phase.
2. Description of the Related Art
Hitherto, gas chromatography, etc., has been used to detect substances contained in a vapor phase, and various substance concentrations in a sampled gas are detected. However, the chromatography method basically requires that human beings should sample specimens. It is not suited for automatically detecting substances in a vapor phase.
A vapor phase sensor is known which comprises a plurality of electrodes, whose electrical conditions (normally, potential and current depending on oxidation-reduction potential change) change according to the substance concentration, etc., in a phase. The electrodes are installed in a vapor phase and the electrical conditions of the electrodes are detected for determining the substance amount in the vapor phase. Such a vapor phase sensor can be used to detect the concentration of any desired gas simply by installing the sensor in the detected atmosphere. The concentration of the gas to be measured can also be measured by using films, membranes, etc., having gas selectivity.
Such vapor phase sensors are described in Japanese Patent Laid-Open Nos. Hei 5-10905, 5-60727, 5-45321, etc., for example.
However, in detection of chemical substances by such conventional sensors, basically only a potential or current change is measured. The concentration of a single gas or a total potential or current change of gases can only be measured by one sensor, and substances contained in a vapor phase cannot be identified.
By the way, freshness of various foods is often estimated from factors such as the storage condition (freezing, cold storage) and the number of storage days of the foods. On the other hand, very fresh beef is not necessarily good while mature beef is preferred as food. In the final stage of the distribution process, frozen beef is not simply thawed, but placed under control at predetermined temperature and humidity in a thawing and maturing chamber for providing mature beef.
However, the degree of maturity varies depending on the condition of the frozen beef before its freezing, etc. At this time, human beings inspect the condition of thawed beef to determine the degree of maturity. Such judgement by human beings leads to inefficient work and moreover varies depending on the individual. Therefore, it is desired to measure the degree of maturity (freshness) easily and rapidly.
The measurement needs to be made while being out of contact with the food to comply with regard to the food hygiene management laws etc., and in such a way that the food is not destroyed while being measured during quality control.